i believe you could squeeze 2 18's in a normal imperial. imo, the normal imperial would be your best bet. at least it will out-perform the so because each has diffrent design goals. the so is supposed to go really low and the normal imp is supposed to get loud.

In that space I would personally do 8 imperials with 1 18" per box.That is one heckuva lot of wood and construction, but I think the overall yeild would be a lot more efficient and you could get a lot more from placement and out of less amplifier power. Of course there are a lot of things to consider.8 18" subs is a lot for any space lol.But overkill means more headroom and more headroom means the equipment lasts longer.4 IMPS with 2 15s per would probably fill the club with plenty low end. I agree that the normal IMP would be the way to go too. The SO will likely be tuned so low that you won't get much from it in that space.Now how about those tickets to Canada? Need some muscles to move around 8 IMPS? lol

I guess Steve would be the proper person to ask about the 18", but the way I see it is this. Steve's white paper says that two drivers is optional (15") meaning you can build it for either one driver or two. 1 18 is not equivalent in cone to two 15s, but obviously more than 1. That would tell me that it should fall in the middle. He also says that he used one in a night club with a single 12 inch sub in a sealed enclosure firing into the opening where the normal speaker was supposed to go and it just pounded.If you are using this as sub only, I would think the higher tuning you would get from a larger driver in the classic box would be ideal.Again, I have not the experience to answer succesfully, but my thinking would lead me to believe that this is the way to go.Good luck with it! If things go my way, I will be traveling to Thunder Bay, Ontario in the not so distant future. Maybe while I am over the border and making trips, I could make a stop to throw one or two back with ya and pour over Imp plans!

Good luck! Let us know what equipment you are actually going to use too!

There was a post on the original Imperial thread where someone built an imperial and put in two 18's. They also cracked the drywall in their listening room after the first test run. Two 15s fit nicely in the ones I built. Two 18s seems like it would be tight and may depend on the driver you choose whether it'll fit or not. I know that two 15s work, from experience. I suspect one 18 would be a good setup also, and maybe cheap for the drivers than two 15s.

Keep us posted. Or maybe we'll just feel it when you fire those subs up the first time!

2 x 18's fit nicely if you add another baffle board (so the baffle board is now 1.5" thick). The new baffle board should go full width, so its 1.5" wider than the baffle board thats underneath. This buys you an extra 1.5" of wood for what remains after you cut the speaker holes out. And believe me, 1.5" makes all the difference in the world there. Here's the link to my picture...

that's dual 18's in the Imperial...notice how the front baffle board is full width and how little wood is left between and on the edges of the speakers. It is a standard size Imperial in every dimension, its just that a 2nd baffle board has been added. And when you do it, you will notice that the Imperial was almost designed to take a 2nd baffle board.

Also, be sure to try turning the Imperials around and firing them into a corner once you start figuring out where to place them. You will be amazed at how much more output you can get.

I like that idea Dank!That way you would also be protecting some expensive hardware from potential drinking tomfoolery and you would have the opening to the horn protected from flying beer cans and the like.I can only imagine the LOW frequencies this thing would produce with the Fs of the 18's and 1/8th space loading!WOW

If you are close to Mpls. MN or are passing by you can stop on over and listen to my pair of dual 18 Imperials. I may even be interested in selling them if you are interested. Might be worth a trip to make sure they will do what you want before you start building. Lets see...8 Imperials at 5 sheets of plywood each, thats 40 sheets of plywood at $40...thats $1600 for the wood, then you add...well, you get the point.

Four Imperials with two 18" drivers each would produce a shocking amount of bass. I think eight would be overkill, although, perhaps that's the intent.

I suggest you build one pair first and see how they sound. Maybe the experiment will stop right there. Even if you still want to build the others you will learn things in the first build that will make the following ones easier.

Dank Thats a really good Idea ... I'd love to hear a pair ... but I'm jumping in blind! N if I make a pair and it's not good for the Club .. well I put em in my shop!! I don't think my wife would let me put em in the house ... lol